feat: Customize Retry Initial Packet behavior

[gaukas]

It is implementation-specific that when the server is not responding to QUIC Initial Packets carrying ClientHello messages, how often does the QUIC client retry by sending a new Initial Packet with a greater (by how many?) Packet Number, as well as how many retry will be made in total before the client gives up.

This could be trivially fingerprint-able and should be considered in designing a QUIC parrot.